J. R. C. Jansen

Predicting cardiac output responses to passive leg raising by a PEEP-induced increase in central venous pressure, in cardiac surgery patients

BACKGROUNDnChanges in central venous pressure (CVP) rather than absolute values may be used to guide fluid therapy in critically ill patients undergoing mechanical ventilation. We conducted a study comparing the changes in the CVP produced by an increase in PEEP and stroke volume variation (SVV) as indicators of fluid responsiveness. Fluid responsiveness was assessed by the changes in cardiac output (CO) produced by passive leg raising (PLR).nnnMETHODSnIn 20 fully mechanically ventilated patients after cardiac surgery, PEEP was increased +10 cm H2O for 5 min followed by PLR. CVP, SVV, and thermodilution CO were measured before, during, and directly after the PEEP challenge and 30° PLR. The CO increase >7% upon PLR was used to define responders.nnnRESULTSnTwenty patients were included; of whom, 10 responded to PLR. The increase in CO by PLR directly related (r=0.77, P<0.001) to the increase in CVP by PEEP. PLR responsiveness was predicted by the PEEP-induced increase in CVP [area under receiver-operating characteristic (AUROC) curve 0.99, P<0.001] and by baseline SVV (AUROC 0.90, P=0.003). The AUROCs for dCVP and SVV did not differ significantly (P=0.299).nnnCONCLUSIONSnOur data in mechanically ventilated, cardiac surgery patients suggest that the newly defined parameter, PEEP-induced CVP changes, like SVV, appears to be a good parameter to predict fluid responsiveness.

A comparison of stroke volume variation measured by the LiDCOplus and FloTrac-Vigileo system

The aim of this study was to compare the accuracy of stroke volume variation (SVV) as measured by the LiDCOplus system (SVVli) and by the FloTrac‐Vigileo system (SVVed). We measured SVVli and SVVed in 15 postoperative cardiac surgical patients following five study interventions; a 50% increase in tidal volume, an increase of PEEP by 10u2003cm H2O, passive leg raising, a head‐up tilt procedure and fluid loading. Between each intervention, baseline measurements were performed. 136 data pairs were obtained. SVVli ranged from 1.4% to 26.8% (mean (SD) 8.7 (4.6)%); SVVed from 2.0% to 26.0% (10.2 (4.7)%). The bias was found to be significantly different from zero at 1.5 (2.5)%, pu2003<u20030.001, (95% confidence interval 1.1–1.9). The upper and lower limits of agreement were found to be 6.4 and −3.5% respectively. The coefficient of variation for the differences between SVVli and SVVed was 26%. This results in a relative large range for the percentage limits of agreement of 52%. Analysis in repeated measures showed coefficients of variation of 21% for SVVli and 22% for SVVed. The LiDCOplus and FloTrac‐Vigileo system are not interchangeable. Furthermore, the determination of SVVli and SVVed are too ambiguous, as can be concluded from the high values of the coefficient of variation for repeated measures. These findings underline Pinsky’s warning of caution in the clinical use of SVV by pulse contour techniques.

Comprehensive review: Is it better to use the Trendelenburg position or passive leg raising for the initial treatment of hypovolemia?

Hypovolemia is a common clinical problem. The Trendelenburg position and passive leg raising (PLR) are routinely used in the initial treatment while awaiting fluid resuscitation. In this meta-analysis, we evaluated the hemodynamic effects of PLR and Trendelenburg positioning to determine which position had the most optimal effect on cardiac output (CO). Databases were searched for prospective studies published between 1960 and 2010 in normovolemic or hypovolemic humans; these studies had to investigate the hemodynamic effects within 10 minutes of a postural change from supine. Twenty-one studies were included for PLR (n=431) and 13 studies for Trendelenburg position (n=246). Trendelenburg position increased mean arterial pressure (MAP). Cardiac output increased 9%, or 0.35 L/min, at one minute of head-down tilt. Between 2 and 10 minutes, this increase in CO decreased to 4%, or 0.14 L/min, from baseline. Cardiac output increased at one minute of leg elevation by 6%, or 0.19 L/min. The effect persisted after this period by 6%, or 0.17 L/min. Both Trendelenburg and PLR significantly increased CO, but only PLR seemed to sustain this effect after one minute. Although the Trendelenberg position is a common maneuver for nurses and doctors, PLR may be the better intervention in the initial treatment of hypovolemia.

Mean cardiac output by thermodilution with a single controlled injection.

ObjectiveA new method to estimate mean cardiac output by thermodilution with a single duration-controlled injection was evaluated in patients. DesignProspective criterion standard study. SettingUniversity hospital cardiac surgical intensive care unit and cardiac operation room. PatientsOf 33 patients, 24 underwent coronary bypass graft surgery, four had a valve replacement, and five were treated in the intensive care unit. InterventionsInterventions consisted of thermodilution cardiac output measurements. One single duration-controlled injection of cold fluid was used to calculate cardiac output. This controlled injection was performed with a duration equal to one whole ventilation cycle of the ventilator. An algorithm adapted to this duration-controlled injection calculated cardiac output. Moreover, this algorithm has properties to reduce errors caused by artificial ventilation and thermal noise. Measurements and Main Results In 33 patients, the averaged values of four measurements equally spread over the ventilatory cycle (phase-controlled) were compared with the values of two single duration-controlled measurements. The measurements were performed during periods of stable respiration and circulation. No significant difference was observed between the mean of four phase-controlled measurements and the mean of the two duration-controlled measurements. The cardiac output values in the intensive care patients were significantly higher compared with the two other patient groups (p < .05). The difference between the two methods could not be subdivided for the three patient groups (p > .05). The coefficient of variation of the single duration-controlled thermodilution measurements was significantly lower than the single phase-controlled measurements, 3% vs. 6% (p < .01). ConclusionsOne single duration-controlled injection thermodilution measurement is as accurate and repeatable as the mean of four phase-controlled measurements and is clinically feasible.

Developmental morphometry and physiology of the rabbit vagus nerve

The morphological and physiological features of the rabbit vagus nerve were studied at different ages after birth. The total fibre count is about 37,500 of which at birth 1-2% and in the adult animal approximately 10% are myelinated. In the postnatal period the cross-sectional area of the vagus grows to 5 times its perinatal size due to an increase of endoneural collagen, fibre growth and myelinization. The myelinization is most pronounced in the first 2 weeks after birth, axonal growth is predominant thereafter. The available data suggest that the begin of myelinization as well as the subsequent development of the myelin sheath are not dependent on axonal size. There seems to be no fundamental difference between the morphological development of the vagus and other peripheral nerves, e.g. the sciatic nerve of the rat. At birth the vagus nerve contains 2 fibre groups as can be measured from the compound action potential with conduction velocities of 11.4 and 0.9 m.s-1 respectively. Upon subsequent development the conduction velocity of these fibres increases to 31.9 and 1.2 m.s-1 in full-grown animals. THe compound action potential of the adult nerve implies 2 additional fibre groups with conduction velocities of 12.3 and 4.6 m.s-1 respectively. These two fibre populations develop gradually from 1 to 2 weeks after birth and arise probably from the slowest conducting, non-myelinated or C-fibres. It is concluded that the functional innervation of the sinoauricular node may be operational at birth as far as the cervical vagus nerve is concerned.

Cardiac Output by Thermodilution and Arterial Pulse Contour Techniques

A reliable method of cardiac output monitoring is particularly desirable in patients in the intensive care unit (ICU) and in patients undergoing cardiac, thoracic, or vascular interventions. As the patient’s hemodynamic status may change rapidly, continuous monitoring of cardiac output will provide information allowing rapid adjustment of therapy. Over the years, there has been a continuing development of new methods and devices to measure cardiac output, but none of these methods has gained unrestricted acceptance. Only the conventional thermodilution method has been generally accepted and is currently the clinical standard to which all other methods are compared. However, this method can only provide mean cardiac output if three or more single estimates are averaged, because individual thermodilution estimates show substantial scatter [1–4]. Also, the ‘recent breakthrough’ [5–9] of the ‘old’ transpulmonary thermodilution [10–13], as an alternative to the pulmonary artery catheter (PAC), needs three measurements to be averaged to reach sufficient precision. Three measurements with this system consume approximately 3 minutes. Therefore, these two thermodilution methods lack the ability to monitor cardiac output continuously. There are eight desirable characteristics for cardiac output monitoring techniques [14]: accuracy, reproducibility or precision, fast response time, operator independency, ease of use, continuous use, cost effectiveness, and no increased mortality and morbidity. Unfortunately, a technique which combines these eight characteristics has not become available yet. Consequently, in clinical practice the cardiac output measurement technique used varies depending on the preference of the treating physician and the available equipment.

Breath-to-breath analysis of abdominal and rib cage motion in surfactant-depleted piglets during high-frequency oscillatory ventilation

ObjectiveTo assess the value of monitoring abdominal and rib cage tidal displacement as an indicator of optimal mean airway pressure (Paw) during high-frequency oscillatory ventilation (HFOV).Design and settingProspective observational study in a university research laboratory.AnimalsEight piglets weighing 12.0±0.5xa0kg, surfactant depleted by lung lavage.InterventionsCompliance of the respiratory system (Crs) was calculated from a quasistatic pressure volume loop. After initiation of HFOV lung volume was recruited by increasing Paw to 40xa0cmH2O. Then mean Paw was decreased in steps until PaO2/FIO2 was below 100xa0mmHg. Proximal pressure amplitude remained constant.Measurements and resultsAbdominal and rib cage tidal displacement was determined using respiratory inductive plethysmography. During HFOV there was maximum in tidal volume (Vt) in seven of eight piglets. At maximal mean Paw abdominal and rib cage displacement were in phase. Phase difference between abdominal and rib cage displacement increased to a maximum of 178±28° at minimum mean Paw. A minimum in abdominal displacement and a maximum of Vt was found near the optimal mean Paw, defined as the lowest mean Paw where shunt fraction is below 0.1.ConclusionsDuring HFOV abdominal and rib cage displacement displayed mean Paw dependent asynchrony. Maximal Vt and minimal abdominal displacement coincided with optimal Crs, oxygenation, and ventilation, suggesting potential clinical relevance of monitoring Vt and abdominal displacement during HFOV.

The effect of propofol on haemodynamics: cardiac output, venous return, mean systemic filling pressure, and vascular resistances

BACKGROUNDnAlthough arterial hypotension occurs frequently with propofol use in humans, its effects on intravascular volume and vascular capacitance are uncertain. We hypothesized that propofol decreases vascular capacitance and therefore decreases stressed volume.nnnMETHODSnCardiac output (CO) was measured using Modelflow(®) in 17 adult subjects after upper abdominal surgery. Mean systemic filling pressure (MSFP) and vascular resistances were calculated using venous return curves constructed by measuring steady-state arterial and venous pressures and CO during inspiratory hold manoeuvres at increasing plateau pressures. Measurements were performed at three incremental levels of targeted blood propofol concentrations.nnnRESULTSnMean blood propofol concentrations for the three targeted levels were 3.0, 4.5, and 6.5 µg ml(-1). Mean arterial pressure, central venous pressure, MSFP, venous return pressure, Rv, systemic arterial resistance, and resistance of the systemic circulation decreased, stroke volume variation increased, and CO was not significantly different as propofol concentration increased.nnnCONCLUSIONSnAn increase in propofol concentration within the therapeutic range causes a decrease in vascular stressed volume without a change in CO. The absence of an effect of propofol on CO can be explained by the balance between the decrease in effective, or stressed, volume (as determined by MSFP), the decrease in resistance for venous return, and slightly improved heart function.nnnCLINICAL TRIAL REGISTRATIONnNetherlands Trial Register: NTR2486.

Non-invasive continuous arterial pressure and pulse pressure variation measured with Nexfin® in patients following major upper abdominal surgery: a comparative study

We compared the accuracy and precision of the non‐invasive Nexfin® device for determining systolic, diastolic, mean arterial pressure and pulse pressure variation, with arterial blood pressure values measured from a radial artery catheter in 19 patients following upper abdominal surgery. Measurements were taken at baseline and following fluid loading. Pooled data results of the arterial blood pressures showed no difference between the two measurement modalities. Bland–Altman analysis of pulse pressure variation showed significant differences between values obtained from the radial artery catheter and Nexfin finger cuff technology (mean (SD) 1.49 (2.09)%, p < 0.001, coefficient of variation 24%, limits of agreement −2.71% to 5.69%). The effect of volume expansion on pulse pressure variation was identical between methods (concordance correlation coefficient 0.848). We consider the Nexfin monitor system to be acceptable for use in patients after major upper abdominal surgery without major cardiovascular compromise or haemodynamic support.

Ventilator-induced central venous pressure variation can predict fluid responsiveness in post-operative cardiac surgery patients

Ventilator‐induced dynamic hemodynamic parameters such as stroke volume variation (SVV) and pulse pressure variation (PPV) have been shown to predict fluid responsiveness in contrast to static hemodynamic parameters such as central venous pressure (CVP). We hypothesized that the ventilator‐induced central venous pressure variation (CVPV) could predict fluid responsiveness.